With an ever increasing number of people purchasing recreational vehicles, for safety, it is very important that stability between a towing vehicle and a trailer be maintained while traveling at turnpike speeds. One form of instability exhibited by tow vehicles-trailers combination is trailer sway. Swaying causes the trailer to oscillate back and forth in a manner similar to the oscillation of pendulum. This instability results in severe yawing in the trailer which can lead to loss of steering control of the towing vehicle.
To alleviate sway instability, some larger trailers are equipped with damping or spring devices attached to the hitch. These damping devices normally consists of at least one shock absorber located on each side of the tongue of the trailer. These devices improve trailer sway control at speeds slower than the desired speed for normal highway driving.
In addition, stiffening of the sidewalls of the tires on trailers helps to dampen some of the sway forces when traveling at low speeds. However, it has been found that at high speeds the damping characteristics of the tires have little overall effect on the total oscillatory movement of the trailer.
In U.S. Pat. No. 3,893,692, incorporated herein by reference, an anti-sway apparatus is disclosed which has a comparator means that compares lateral movement of the front of a trailer with that at the rear. Whenever oscillatory forces in a trailer reach a predetermined value the comparator supplys an actuation signal which momentarily operates a brake applying servomotor. The anti-sway apparatus includes a first sensor located at the front and a second sensor located at the rear of the trailer. The first and second sensors supply the comparator means which is located at the center of gravity of the trailer with signals representative of the lateral movement in the trailer. As long as the first and second sensors supply the comparator means with substantially the same signal, the comparator means remains inactive. Whenever the first and second sensors supply the comparator means with different signals, the anti-sway apparatus is activated. Activation of the antisway apparatus develops a brake signal which operates the brake applying servomotor. Operation of the brake applying servomotor supplys the wheel brakes in the trailer with a braking signal. Unfortunately, under some conditions the intensity of the brake signal from the anti-sway apparatus causes the servomotor to be activated at such a speed that the wheel brakes in the trailer lock. When the trailer wheels are locked, another instability condition is created between the tow vehicle and the trailer.